Flow measuring apparatus

ABSTRACT

Flow metering apparatus comprising an elongate cylindrical element mounted in the stream of flowing fluid to produce Karman&#39;&#39;s vortices, the element being formed on opposite sides thereof with openings leading into corresponding interior cavities coupled together within the element; pressure conduits connect from each of the interior cavities to a sealed pressure chamber outside of the stream of flowing fluid and containing a flow-responsive detecting device including an electrically-heated wire adapted to develop electrical pulses corresponding to the pressure pulses produced by the shedding of Karman&#39;&#39;s vortices.

United States Patent [1 1 Yamasaki et al.

[ Mar. 27, 1973 FLOW MEASURING APPARATUS [75] Inventors: Hiroo Yamasaki;Yoshio Kurita,

both of Tokyo, Japan [73] Assignee: Yokogawa Electric Works, Ltd.,

Tokyo, Japan [22] Filed: Jan. 22, 1971 [21] Appl. No.: 108,731

[30] Foreign Application Priority Data Jan. 30, 1970 Japan ..45/3l96[52] U.S.- Cl. ..73/194 B [51] Int. Cl ..G01f 1/00, GOlp 5/00 [58] Fieldof Search ..73/l94 B [56] References Cited UNITED STATES PATENTS3,564,915 2/1971 Tomota et al. ..73/l94 3,279,251 10/1966 Chanaud....73/204 X 3,559,482 2/1972 Baker et a1. ..73/204 OTHER PUBLICATIONSSharpsteen Fluid Amplifier Measures Flow Velocity in Control EngineeringJanuary 1966 pg. 103.

Primary ExaminerRichard C. Queisser Assistant Examiner-Herbert GoldsteinAttorney-Bryan, Par-melee, Johnson & Bollinger ABSTRACT Flow meteringapparatus comprising an elongate cylindrical element mounted in thestream of flowing fluid to produce Karmans vortices, the element beingformed on opposite sides thereof with openings leading intocorresponding interior cavities coupled together within the element;pressure conduits connect from each of the interior cavities to a sealedpres sure chamber outside of the stream of flowing fluid and containinga flow-responsive detecting device including an electrically-heated wireadapted to develop electrical pulses corresponding to the pressurepulses produced by the shedding of Karmans vortices.

6 Claims, 11 Drawing Figures zl zaqlllq lg l FLOW MEASURING APPARATUSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to flow metering apparatus of the type wherein a cylindricalobject in a stream of flowing fluid produces a wake including a distinctpattern of vortices known as the Karmans vortex street. The vortices areshed from alternate sides of the object in a periodic manner. It hasbeen found that there is a definite relationship between the frequency fof shedding of the vortices, the diameter D of the cylinder, and thevelocity V of the stream, expressed by:

f= Khu. (V/D) Accordingly, it is possible to determine the flow velocityv by measuring the frequencyfof the generation of vortices.

2. Description of the Prior Art Various arrangements have been proposedfor producing signals responsive to the rate of development of Karmansvortices as described above. In one such arrangement shown on page 103of the January, 1966, issue of Control Engineering, a fluidic flip-flopserves as the pressure detection device, and is located within thecylindrical element in the flowing stream to sense the pressurefluctuations directly. Sensing ports of the flip-flop open out into theflowing fluid adjacent the surface of the cylinder, such that theflip-flop state is alternated by the alternating formation of vorticesat the surface.

In still another prior art arrangement, disclosed in copendingapplication Ser. No. 760,604, filed Sept. 18, 1968, by Miaji Tomota, etal., the cylindrical element is formed with a transverse bore containinga detection device comprising a pressure-responsive diaphragm forsensing pressure fluctuations and for developing output signalsresponsive to the shedding of Karman s vortices. Various other internalpressure detection arrangements are disclosed in that co-pendingapplication.

Such prior art apparatus of the general type referred to above has notbeen fully satisfactory for certain applications. For example, therehave been some difficulties in maintaining the detection devicesproperly operative in flowing streams containing contaminants. Also,there have been problems with maintenance, particularly with regard todisassembly of the apparatus and replacement of portions thereof.

SUMMARY OF THE INVENTION In a preferred embodiment of the invention tobe described hereinbelow in detail, the cylindrical element inserted inthe flowing stream is formed on opposing sides with holes leading tocorresponding cavities within the element. To detect the pressurevariations produced by the shedding of Karmans vortices, the cylindricalstructure is formed internally with pressure conduits leading from thecavities to opposite ends of a chamber located outside the stream offlowing fluid. This chamber contains a flow-responsive detection device,for example in the form of an electricallyheated wire. The overallarrangement affords effective isolation between the detection device andthe stream of flowing fluid, particularly so as to protect the detectorfrom the contaminating effects of material carried in the flowingstream. The arrangement further is advantageous in accommodating readydisassembly of the. equipment for maintenance or for replacement ofindividual parts.

Accordingly, it is a principal object of this invention to provideimproved apparatus and techniques for sensing the shedding of Karmansvortices and thereby to measure the rate of fluid flow. It is a specificobject of the invention to provide control apparatus which reduces thecontaminating effects of the flowing fluid stream. Still another objectof the invention is to provide flow measuring apparatus of the typedescribed which is more suitable for commercial use.

Other objects, aspects and advantages of the invention will be pointedout in, or apparent from, the detailed description hereinbelow,considered together with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustrationof the mode of formation of Karmans vortices;

FIG. 2 is a vertical longitudinal section through a fluid flow pipe,showing one form of the cylindrical element in elevation;

FIG. 3 is a cross-section taken along line 33 of FIG. 2;

FIG. 4 is a horizontal detail section taken along line 4'4 of FIG. 3;

FIG. 5 is a view similar to FIG. 2, but showing a modified form ofcylindrical element;

FIG. 6 is a view like FIG. 2, but of still another form of cylindricalelement;

FIG. 7 is a cross-section taken along line 7--7 of FIG. 6;

FIG. 8 is a horizontal detail section taken along line 8-8 of FIG. 7;

FIG. 9 is a view like FIG. 6, but showing a modified version of thecylindrical element;

FIG. 10 is a vertical section showing a modified form of sensing moduleadapted to be coupled to any of the cylindrical elements disclosed; and

FIG. 11 is a vertical section showing a further modified version of asensing module. I

Referring first to FIG. 1, it is known that the insertion of acylindrical element 10 in a stream of flowing fluid F results in theperiodic formation and shedding of vortices from alternate sides of theelement. Such element typically is secured in place by attachment to thewall of the pipe 12, as shown in FIG. 2.

Referring now also to FIGS. 3 and 4, the element 10 is formed onopposite sides thereof with respective sets of holes 14 and 16. Each setof holes is arranged in a straight line parallel to the axis of thecylinder, and communicates with a corresponding interior cavity 18, 20.These cavities are separated by a central partition 22 having an opening24 serving as a passageway to accommodate the flow of fluidtherebetween.

When the vortices are shed from element 10, corresponding pressurefluctuations are produced next to the adjacent set of holes 14 and 16.Since the vortices are shed alternately from the opposite sides of theelement, the pressures within the cavities 18, 20 also will fluctuate inan alternating fashion. These pressure fluctuations cause fluid to bedisplaced (i.e. to flow) through the opening 24 in an alternatingfashion, first in one direction and then in a reverse direction, asindicated by the arrows a and h. The rate of pressure alternation isproportional to the rate of generation of vortices, and this in turn isproportional to the rate of fluid flow through the pipe.

To produce an external indication of the rate of pressure alternation,the two cavities 18, 20 are coupled by respective pressure conduits 26,28 to an external sensor modulegenerally indicated at 32, and locatedbeyond the pipe wall. This sensor module thus may be arranged as aseparate unit, removably secured to the cylindrical element 10, i.e.readily disconnectable therefrom. Suitable fittings typically will beprovided at the place where the element passes through the pipe wall, tosecure the element firmly in place, and preferably to seal the openingthrough the pipe wall. Since such fittings are conventional, to simplifythe drawings the structure is illustrated in schematic for mat. For thesame reason, the mode of attaching the module to the cylindrical elementis not shown in detail, but it will be understood that such attachmentprovides for proper fluid-tight seals where the conduits 26, 28 passbetween the module and the cylindrical element.

Within the sensor module 32 the two conduits 26, 28 lead to oppositeends of asmall fluid-tight pressure chamber 34 containing a flow-sensingor detecting device 36. In one preferred embodiment, the detectingdevice is a known arrangement comprising an electrically-heatable wirethe ends of which are connected to external terminals 38, 40. Theseterminals are adapted to be coupled to a conventional sensing circuit(not shown) which produces a flow of electric current through the wire,and also measures the change in resistance of the wire resulting fromdisplacement of the fluid accompanying the alternations in fluidpressure in the two cavities 18, 20.

This arrangement is particularly advantageous in that it maintains thedetecting device 36 substantially out of contaminating contact with theflowing fluid F, and thus reduces the possibility of damage to thedetector due to coating by contaminants or other adverse effect. Also,this arrangement permits ready disassembly of the principal flow metercomponents for purposes of checking their operation, cleaning offforeign matter which has built up on the cylindrical element, orreplacing any part which is not functioning properly.

As shown in FIG. 5, the cylindrical element A can be secured to bothopposite walls of the pipe 12, for applications where such anarrangement is appropriate.

FIGS. 6-8 show an alternate embodiment wherein the cylindrical element108 is formed on opposite sides with elongate slots 14B, 16B to providecommunication between the vortex pressure fluctuations and interiorcavities 18B, 203. The structure of element 108 is substantially greaterin wall thickness than that of the FIG. 2 embodiment, and the pressureconduits 26B, 28B open out in the region of the slots 14B, 16B. It willbe understood, however, that each slot provides mutual communicationwith both the corresponding cavity and the associated pressure conduit,so that pressure fluctuations from the shedding of vortices aretransmitted to the chamber 34 as in the previously described embodiment.FIG. 9 shows an alternate construction wherein the element 10C issecured at both ends to the pipe 12.

Referring now to FIG. 10, for some applications it may be desirable toprovide sealing means in the pressure conduits 26D, 28D, to effectpositive isolation between the chamber 34D and the fluid flowing pastthe cylindrical element to which the sensor module 32D is connected. Inthe FIG. 10 embodiment, this is provided by use of a sealing fluid 50which is lighter than the fluid being measured, and therefore remains upin the region of the chamber 34D so as to provide a positive seal toisolate the chamber from the fluid being measured. The conduits 26D, 28Dmay be formed with enlarged isolation sections 52, 54 to contain thebulk of the sealing fluid.

Other forms of sealing means can be provided to effect positive physicalisolation of the fluid F from the detecting device while assuring thatpressure fluctuations are transmitted from the vortices to the chamber34 without significant attenuation. One other such arrangement is shownin FIG. 11, wherein sealing fluid 56 is provided which is heavier thanthe fluid F being measured. In this embodiment, the chamber 34B islocated near the lower regions of the isolation sections 52, 54 so as toinsure that the heavier fluid remains at all time in contact with thedetection device 36. The conduits 26E, 28E are provided with verticalextensions 60, 62 which open out above the level of the fluid 56. Thede,- tection device 36 in this embodiment comprises apressure-responsive cell, of conventional construction, adapted toproduce output pulses in response to fluctuations in the pressure of thesurrounding fluid.

Both of the embodiments of FIGS. 10 and l 1 may be provided withshut-off valves 64, 66 to temporarily close off the pressure conduits,for example, while removing the sensor module 32 during maintenanceprocedures or the like. It may also be noted that a sealing fluid can beemployed in the embodiments shown in FIGS. 3 and 7, eg in the conduitportions located in the sensor module. Similarly, shut-off valves can beincluded in such sensor module to close off the fluid channels while themodule is disconnected from the cylindrical element 10. The shut-offvalves can be made so as to operate automatically whenever the module isremoved.

Although specific embodiments of the invention have been disclosedherein in detail, it is to be understood that this is for the purpose ofillustrating the invention, and should not be construed as necessarilylimiting the scope of the invention, since it is apparent that manychanges can be made to the disclosed structures by thoseskilled in theart to suit particular applications.

We claim:

1. In fluid flow metering apparatus of the type wherein an elongatecylindrical element is inserted in a stream of fluid to produce atopposite sides of the element vortices which are shed in an alternatingfashion vwith a frequency bearing a predetermined relationship to thevelocity of the fluid stream, and wherein the inserted element is formedwith interior cavities communicating with said fluid stream throughopenings at said opposite sides, said cavities being connected by aninternal passageway permitting fluid to flow between said cavities andthrough said openings in an alternating fashion corresponding to theshedding of vortices, and wherein detection means are provided fordetecting the frequency of vortex production to provide a measure of thevelocity of the fluid stream;

that improvement in such apparatus which com- ,prises:

pressure conduit means at least partly within said element connectingsaid cavities together through a fluid channel which is separate anddistincti from said internal passageway, said fluid channel extendingthrough a region which is remote from said cavity openings and alsoremote from said internal passageway, said pressure conduit meanstransmitting through said fluid channel to the remote region alternatingfluid fluctuations produced by and corresponding in frequency to theshedding of vortices from said element;

said detection means being located in said fluid channel in the remoteregion of said pressure conduit means and being responsive to the fluidfluctuations therein produced by the shedding of vortices adjacent saidopposite sides of said element, whereby the detection means in saidremote region remains substantially free of contaminants in the fluidstream; and

sealing means between said openings and said pressure conduit region toisolate said detector from said fluid while permitting transmission tothe detector of the fluid fluctuations produced by the shedding ofvortices.

2. Apparatus as claimed in claim 1, wherein said sealing means comprisesa sealing fluid in said pressure conduits.

3. Apparatus as claimed in claim 2, wherein said detection means islocated within said sealing fluid.

4. In fluid flow metering apparatus of the type wherein an elongatecylindrical element is inserted into a flow pipe carrying a stream offluid, said element producing at opposite sides thereof vortices whichare shed in an alternating fashion with a frequency bearing apredetermined relationship to the velocity of the fluid stream in thepipe, the inserted element being formed with interior cavitiescommunicating with said flowing fluid through openings at said oppositesides, the apparatus including detection means for detecting thefrequency of vortex production to provide a measure of the velocity ofthe fluid stream in the pipe;

the improvement in such apparatus which comprises: pressure conduitmeans at least partly within said element connecting said cavitiestogether through a region which is remote from said cavity openings,said pressure conduit means transmitting to the remote regionalternating fluid fluctuations produced by and corresponding infrequency to the shedding of vortices from said element; said detectionmeans being located in the remote region of said pressure conduit meansand being responsive to the fluid fluctuations therein produced by theshedding of vortices adjacent said opposite sides of said element; andsealing means to isolate said detection means from said openings whilepermitting the transmission of pressures between said openings and saiddetection means; whereby the detection means in said remote regionremains substantially free of contaminants in the fluid stream.

5. Apparatus as claimed in claim 4, wherein said sealing means comprisesa sealing fluid in said pressure conduits.

6. Apparatus as claimed in claim 5, including valve means in saidpressure conduits to provide for shutting off fluid communicationbetween said openings and said detection means.

1. In fluid flow metering apparatus of the type wherein an elongatecylindrical element is inserted in a stream of fluid to produce atopposite sides of the element vortices which are shed in an alternatingfashion with a frequency bearing a predetermined relationship to thevelocity of the fluid stream, and wherein the inserted element is formedwith interior cavities communicating with said fluid stream throughopenings at said opposite sides, said cavities being connected by aninternal passageway permitting fluid to flow between said cavities andthrough said openings in an alternating fashion corresponding to theshedding of vortices, and wherein detection means are provided fordetecting the frequency of vortex production to provide a measure of thevelocity of the fluid stream; that improvement in such apparatus whichcomprises: pressure conduit means at least partly within said elementconnecting said cavities together through a fluid channel which isseparate and distincti from said internal passageway, said fluid channelextending through a region which is remote from said cavity openings andalso remote from said internal passageway, said pressure conduit meanstransmitting through said fluid channel to the remote region alternatingfluid fluctuations produced by and corresponding in frequency to theshedding of vortices from said element; said detection means beinglocated in said fluid channel in the remote region of said pressureconduit means and being responsive to the fluid fluctuations thereinproduced by the shedding of vortices adjacent said opposite sides ofsaid element, whereby the detection means in said remote region remainssubstantially free of contaminants in the fluid stream; and sealingmeans between said openings and said pressure conduit region to isolatesaid detector from said fluid while permitting transmission to thedetector of the fluid fluctuations produced by the shedding of vortices.2. Apparatus as claimed in claim 1, wherein said sealing means comprisesa sealing fluid in said pressure conduits.
 3. Apparatus as claimed inclaim 2, wherein said detection means is located within said sealingfluid.
 4. In fluid flow metering apparatus of the type wherein anelongate cylindrical elemeNt is inserted into a flow pipe carrying astream of fluid, said element producing at opposite sides thereofvortices which are shed in an alternating fashion with a frequencybearing a predetermined relationship to the velocity of the fluid streamin the pipe, the inserted element being formed with interior cavitiescommunicating with said flowing fluid through openings at said oppositesides, the apparatus including detection means for detecting thefrequency of vortex production to provide a measure of the velocity ofthe fluid stream in the pipe; the improvement in such apparatus whichcomprises: pressure conduit means at least partly within said elementconnecting said cavities together through a region which is remote fromsaid cavity openings, said pressure conduit means transmitting to theremote region alternating fluid fluctuations produced by andcorresponding in frequency to the shedding of vortices from saidelement; said detection means being located in the remote region of saidpressure conduit means and being responsive to the fluid fluctuationstherein produced by the shedding of vortices adjacent said oppositesides of said element; and sealing means to isolate said detection meansfrom said openings while permitting the transmission of pressuresbetween said openings and said detection means; whereby the detectionmeans in said remote region remains substantially free of contaminantsin the fluid stream.
 5. Apparatus as claimed in claim 4, wherein saidsealing means comprises a sealing fluid in said pressure conduits. 6.Apparatus as claimed in claim 5, including valve means in said pressureconduits to provide for shutting off fluid communication between saidopenings and said detection means.